Apparatus for irradiating foodstuffs and the like



-DURATION 4 Ndv. 28, 1939. o, ess 2.181293 APPARATUS FOR IRRADIATING FOODSTUFFS AND THE LIKE Fi ledDec. 2, 195a ORR/CK H. 5/665,

INVENTOR.

ATTORNEY.

Patented Nov. 28, 193 9 I UNITED-STATES PATENT OFFICE APPARATUS FOR IRRADIATING FOOD- STUFFS AND THE "LIKE Orrick H. Biggs, Beverly, Mass assignor to Hygrade Sylvania Corporation, Salem, Mass., a corporation of Massachusetts Application December-2, 1938, Serial No. 243,574

6 Claims. (Cl. 62-89) h s invention relates to methods and appara-' relation between intensity and duration of the tus for treating materials by radiation and with sterilizing y particularity to an improved form of sterilizing Figure 4 is a schematic diagram of one form chamber. of timing arrangement;

5 An object of the invention is to provide a Figure 5 is a schematic circuit diagram'of an 5 sterilizing chamber particularly suited to the alternative timing arran nt r ntr llin 0 housing of foods, food products, etc. the radiation lamps according to-the invention;

Another object is to provide an improved reand frigerator having automatically controlled sterilie Fig. 6 is a view of one form of lamp according 10 zation. to the invention. 1 10 A further object is to provide an improved Referring more particularly to Figuresl and 2,

' method of subjecting foods, food products, etc., the numeral I indicates any suitable enclosure to measured radiation by employing sterilizing or housing adapte to contain foods, food-stuffs. radiations of predetermined and repeated duraor similar materia s which tend to change their tion. i taste or chemical characteristics by reasons of 15 A feature of the invention relates to a housing bacteria or' similar organisms. For convenience for foods, food products, etc., having on its inof description it will be assumed that the device I terior a source or sterilizing radiations together is a refrigerator of any well known construction. with means for enhancing the sterilizing action While the drawing shows a refrigerator of the of said radiations. artificial cooling type wherein the cooling unit 2 20 Another feature relates to a refrigerator having is refrigerated by gas, electricity, etc., it will be an interior source of radiations which is rendered understood that any other manner of cooling the automatically eflective forapredetermined durainterior of d v I y be p ye for tion each time a door or similar member is ample, by ice, evaporation, or the like. Furtheropened or closed. 'more, while the drawing shows the refrigerator A further feature relates to a refrigerator or provided with a single main door or access memsimilar device having its interior surface, or at bar 3, it will be understood that any other form least a suitable portion thereof, provided with a of access member, such as a Window or the like, specially designed coating for efficiently diffusing may be provided in addition to the main door 3.

80 and/or reflecting sterilizing radiations such as Suitably mounted within the food,compartment ultra-violet rays or the like. or compartments of the refrigerator are a pair A further feature relates to the organization, of lamps 4, 5, although it will be understood that arrangement and relative location of parts which in this respect the invention is not limited to any go to make up a relatively simple and economical particular, number or disposition of lamps. For

36 sterilizing refrigerator or similar device. example, instead of employing two lamps dis- Other features and advantages not specifically posed on opposite side walls of the refrigerator, v enumerated will-be apparent after a consldera one large lamp. may ,be employed and suitably tion of the following descriptions and the apmounted within the compartment so as to radipended claims. ate uniformly the entire interior of said compart- 4 o While the invention will be disclosed herein as ment. It will also be understood that if the re- 40 embodied in particular forms of apparatus, it .frigerator is provided w th sep ra e fo 00 .'will be understood this is done merely for the partmenta'then one or more lamps may be prop rpose of explaining the invention. While, vided in, each compartment. While, therefore,

therefore, the drawing shows schematically a rethe drawing shows a refrigerator of the single frigerator embodying the invention, it will be apcompartment type provided with shelves 6 and 45 parent that the broad inventive concept can be 1, this is merely for securing simplicity in the embodied in other types of devices without dedrawing. Wherea single lamp or pair of lamps parting from the spirit and scope of the invenis employed as shown in Figures 1 and 3, it is tion. 1 preferable that the shelves be of open-work con- Accordingly, in the drawing Figure 1 is a perstruction so as to allow the sterilizing radiations 50 spective view of a refrigerator embodying fea- -from the lamps to pass therethrough and thus tures of the invention; I enabling the lower and upper portions of the Figure 2 is a sectional view of the refrigerator compartment to be radiated. If. desired, these of Figure l with the door closed; shelves may be of. glass, quartz or other material 5 Figure 3 is a diagrammatic curve showing the which is transparent to the sterilizing radiations.

n the other hand, if non-transparent shelves are employed, then an additional lamp or lamps may bemounted between the shelves to insure suflicient radiation for the entire contents of the compartment.

While the invention is not limited to any particular character of sterilizing radiations, it is preferred to employ radiations in the form of ultra-violet rays between 2500 and 2800 A. (Angstrom units) wave length. More particularly, the lamps 4, may be designed to generate rays having maximum intensity between 2530 and 2540 A. and with substantially negligible radiation above 2800 A.

If desired, the lamps d and 5 may be of the indirect illuminationitype, that is, with their bowl portions provided with a coating which is capable of efilciently reflecting the ultra-violet rays. Thus the inner surface of the bowl portion of each lamp may be provided with a reflecting coating of aluminum in the manner disclosed in 21% U. S. Patent No. 2,123,706, issued July 12,

I have found that the paints or enamels ordinarily employed on the interior of refrigerators are not suitable for conserving orefllciently reflecting ultra-violet rays, and this is probably caused by the fact that ordinary paints or enamels as used in refrigerators absorb a very considerable per cent, of, the ultraviolet rays which are useful for bactericidal purposes. I have found that if the interior of the refrigerator compartment or compartments is provided with a coating which is capable of reflecting to a considerable extent these bactericidal ultra-violet rays, the sterilizing action is improved and it is possible to employ lamps of smaller wattage. Entirely apart from the improved sterilizing action,

therefore, the use of lower wattage lamps for the desired sterilizing action, enables less power to be used in maintaining the temperature of the compartment at a desired value. Thus, as indicated in the drawing, the major portion of the interior of the refrigerator compartment as well as the inner face of the door 3, is provided with a coating of aluminum or other similar material capable of eflioiently reflecting the bactericidal rays. This coating may be applied in any well known manner as by spraying, by the Schoop process, or even by painting and baking. Preferably also, the coating is of diffusely reflecting character so as to reflect the rays as uniformly as possible throughout the entire interior of the compartment.

As pointed out above, one of the most serious drawbacks to the utilization of devices such as ultra-violet lamps on the intgrior of a refrigerator is that such lamps generate a considerable amount of heat, thus reducing the running efliciency of the refrigerator. It is highly desirable, therefore, to employ u tra-violet lamps with as low a wattage as possible consistent with the desired bactericidal action. However, the problem is further complicated by the fact that there is a certain minimum intensity and a certain minimum time below which there is very little effective sterilization. I have found that sterilization by ultra-violet rays of the character set forth herein is normally governed by photo-chemical laws; that is, the total amount of sterilization is directly proportional to intensity and also to duration, so

that for a given degree of sterilization, one-half as much sterilizing intensity is required if the duration is doubled, and vice-versa. However, while this relation is true for a relatively wide range of intensities, at the low intensities there is a threshold value below which the relation does not hold, as indicated by Figure 3, wherein the point P represents this threshold intensity. If, therefore, the lamps 4 and 5 are designed to generate only a low intensity in the neighborhood of this threshold value, there will be considerable chance of the sterilization being ineffective or at least non-uniform. Instead, therefore, of employing low wattage lamps operating for a proportionately long time, I have found that reliable and uniform sterilization can be achieved without undue heat generation by employing relatively high intensity lamps which are allowed to operate intermittently for predetermined fixed intervals, preferably every time the door or other access member is opened and closed. Since low intensity lamps require a relatively long time to achieve satisfactory sterilization, it is entirely possible that foods may be inserted and withdrawn from the-compartment before the necessary sterilizing action hastaken place. This and other disadvantages are overcome by employing sources which produce intensities of bactericidal rays well above the threshold intensity, and which are allowed to operate for a proportionately shorter duration each time the door or other access chamber is closed after the insertion of food material or the like into the compartment.

By employing a narrow-band ultra-violet lamp, the greater part of the electrical energy impressed upon the lamp is transformed into useful bactericidal flux, whereas with ordinary ultra-violet lamps of the broad-band type, a great deal of energy is expended in producing ultra-violet and other rays which are useless for bactericidal purposes and are even detrimental to the taste of the food. By employing relatively high intensity ultra-violet lamps which are designed to produce a relatively narrow band of light wavelengths, e. g., 2500 to 2800 A, and by operating these lamps for predetermined fixed and limited durations each time the door or other access member is closed after the insertion of food material, and by conserving the bactericidal flux through the intermediary of the aluminum coating, it is possible to achieve substantially complete and uniform sterilization of the materials within the food compartment, and with a minimum of undesired heat energy.

While any well known means may be used for timing and limiting the duration of the radiation each time the refrigerator door is closed, there are shown two alternative arrangements in Figures 4 and 5 of the drawing. Referring to Figures 1 and 2, it will be seen that there is mounted with- Spring l2 in turn rotates the commutator l3 which is controlled by a timing escapement (not shown). When the refrigerator door is open the disc I3 is in the position shown in Figure 4 wherein the brush H is out of contact with the metal segment l5. When, however, the spring I2 is wound up due to rod 9 being engaged by the door as above described, the disc [3 is rotated completing the circuit from mains l6 and H to the lamps 4 and 5. Under control of the escapecapement may be adjustably variable so as to vary the period of illumination of the lamps as desired. There is thus provided an arrangement whereby when the refrigerator door is open and then closed, the timing mechanism is set into operation to maintain the ultra-violet lamps lighted for a predetermined fixed interval. It will be understood of course that instead of providing a single semi-circular segment 15, this segment may be replaced by a seriesof separate segments so as to repeatthe illumination of the lamps at predetermined spaced intervals while the disc I3 is rotating.

Instead of employing an escapement which is wound up by a rack and pinion, an ordinary electric clock may be employed, the circuit of which .is completed only when the refrigerator door is contact sets 20 and 2|, 22 and 23, 'insulatingly' mounted on the framework of the refrigerator.

When the door is open the circuits to the relays 24 and 25 are broken. When relay 25 is normal,

the lamps 4' and 5 are disconnected from the mains Z6 and 21. As soon as the door 3 closes, a circuit is completed from main 26, through the lower contacts of relay 24, winding of relay 25,

contacts 2I, l8,20, to the main 21. Relay 25 immediately operates and. causes 'lamps 4 and 5' to light. Relay 25 is preferably of the fast-tooperate siow-to-release type and may take the form of a dashpot relay, a thermostat relay, or

the like. As soon as relay 25 operates, it completes through its lower contacts an operating circuit for relay 24, which upon operating, becomes looked under control of contacts 23, I 9 and 22.

When relay 24 operates it breaks the circuit for relay. 25 which begins to release. After a definite time interval relay 25 completefy restores to normal and breaks the circuit to the lamps which stay dark thereafter until the door is again opened and closed to-repeat the foregoing cycle of operations.

While specific apparatus and circuits are disclosed herein, it will be understood that the invention is not limited thereto and that various changes and modifications may be made therein without departing from the spirit and scope.

of the invention. For example, while the drawing shows lamps 4 and 5 of the spherical bulb type, any other shape of lamp may be employed, for example as illustrated schematically in Figure 6, which represents in half scale size a lamp that has been found to produce the desired results. This lamp comprises in general a tubular body '28 which is evacuated and provided with a filling of compartment to be refrigerated, being started ness.

preferably less than one-half mm. in thick-' The. electrodes 30 and 3| are preferably in the form of molybdenum coils which are sealed into and supported at the ends of the tubes in any well known manner. The particular lamp shown is designed to operate at an impressed voltage of 220 V. A. C. and with a current of 12.5

millianiperes flowing therethrough.

In a lamp of the type described, the electrode drop isgenerally large and fixed, and for that reason it might be thought that making the lamp long, so that the drop in the gas would be as large a proportion as possible of the total drop across the lamp, would be best. However, I have found that where the lamp is operated in a refrigerator the lamp is best made short, so that its length between electrodes is not greater than 3 inches, and is preferably about two inches. This is apparently due'to the ultra-violet output of the lamp being greater at temperatures somewhat above the usual refrigerating temperatures, The lamp temperature is best below 120 F., however.

The shorter lamp operates at a highertemperature. For the same reason the current through the lamp should be at least 40 miiliamperes per square'c'entimeter of discharge tube cross section.

. The current through the lamp will, of course, de-

pend on the voltage of the circuit from which the lamp is operated, and on the ballast resistance or reactance in series with the lamp. The preferable lamp temperature is about A lamp of the type described emits chiefly radiation of about 2536 to 2537 Angstrom units, which is extremely effective for treating foods for sterilization, vitaminization or other .purposes without harming the taste of the ,food. Butter,

lard, meats, milk, and other fatty foods,'which will change'taste markedly before sterilization is obtained when sunlight or a high pressure mercury arc is used for the purpose, will not change taste appreciably underthe influence of the lamp described, even when'the exposure is times that neededfor sterilization. Meat in particular can be kept longer, and at temperatures above the usual refrigeration temperatures, without spoilage. Q g

This application iS' in part 'a continuation of application Serial No. 732,431, filed June 26, 1934, which hasbeen'issued on January 24 1939, as U. S. Patent No. 2,145,196.

The refrigerator temperature generally will be in the neighborhood of 40 Fahrenheit, but may be raised considerably above that if ,desired, sayto 50- Fahrenheit, due to the action, of the ultra'- violet radiation in aiding refrigeration- 'Thermionic electrodes may be used if desired, but in that case it may be necessary, for some foods such as milk, to blacken the glass near the electrodes to prevent the radiationfrom lthe hear ed electrodes falling on the food to be treated. Some foods are easily spoiled by visiblelight.

In a refrigerator of the electrical or mechanical type, where the refrigeration is produced for exampleby compressing a gas in one part of a sealed container, and allowing the gasto expand in another part of the sealed container,-which part is placed in .the compartment to be refrigerated, the compressor is generally driven by an electric motora The motor may be controlled by a switch operated by a thermostat set in the pressure in the gas to be compressed. When the pressure drops, a valve operates the switch which starts the motor, and when the pressure rises sufliciently the valve opens the switch, stopping the motor.

The more often the refrigerator door is opened, the more theair in the refrigerator is changed, and hence the more it necessitates sterilization. I may, therefore, connect the terminals supplying the sterilizing, lamp current directly across the compressor motor terminals, so that when the compressor is running, the lamp operation, and when the compressor is not running the lamp is not operated. Since the more often the refrigerator air is changed, the more often the refrigerator operates, this arrangement is desirable.

If desired, a door switch may be connected in series with the line from the motor to the lamp, to insure that when the refrigerator door is open the lamp is extinguished, thus protecting anyone who may look into the refrigerator, from the ultra-violet rays.

is available, a transformer can be used to get the desired voltage; when direct current must be used, however, the lamp may be connected across the motor armature or commutator, through a transformer if desired.

The sterilizing lamp shown in Figure 6 has its electric terminals at opposite ends of the tube. If desired, the terminals may be brought out at the same end of the tube, the electrode at the opposite end being supported from the terminal end by an insulated metal rod running axially along the center of the lamp tube.

.What I claim is:

1. The combination of an ultraviolet lamp comprising a sealed tubular envelope of Corex glass transmitting radiations at 2537 Angstrom units, an atmosphere of inert gas at low pressure and mercury vapor within said envelope, electrodes about 2 inches apart and within said envelope at each end thereof, apparatus for op-' closing of the door for starting the operation of the lamp, and means actuated by said first mentioned means to extinguish the lamp after a predetermined interval.

2. The combination of an. ultraviolet lamp comprising a sealed tubular envelope of Corex glass transmitting radiations at 2537 Angstrom "units, an atmosphere of inert gas at low pressure and mercury vapor within said envelope, electrodes within said envelope at each end thereof, said electrodes being placed close together to insure heating of the mercury vapor to an efilcient radiating temperature, a refrigerating chamber around said lamp, a door in said refrigerating chamber, means actuated by the closing of the door *for starting the operation of the lamp, and means actuated by said first-mentioned means to extinguish the lamp after a predetermined interval.

3. The combination of a food storage compartment refrigerated to a temperature of about 40 Fahrenheit, apparatus for operating an ultraviolet lamp in said refrigerated compartment at a current density of about 40 milliamperes per square centimeter, and an ultraviolet lamp so operated in said compartment, said lamp comprising a sealed tubular envelope of Corex glass transmitting radiations at 2537 Angstrom units in wavelength, an atmosphere of an inert gas at lowpressure and mercury vapor within said envelope, and electrodes within said envelope at each end thereof, said electrodes being arranged substantially to prevent the emission of visible light from themselves and being spaced no more than 3 inches apart so that the lamp efliciency will be increased by operation above the ambient temperature in the refrigerator.

4. The combination of a compartment refrigerated to a temperature satisfactory for food storage, but inefiicient for operation of a mercury vapor ultraviolet lamp, apparatus for operating a low-pressure close-electrode ultraviolet lamp at a current density suflicient to operate said lamp at a temperature enoughabove the ambient refrigerator temperature to be efficient but not sufficient to increase the electrode temperature to the point where substantial visible light is emitted from the electrodes, an ultraviolet lamp comprising electrodes at each end of a sealed Corex glass tube, transmitting radiation of 2537 Angstrom units wavelength with electrodes within said tube and at each end thereof, said electrodes being placed close together to insure heating of the lamp to a temperature substantially above the ambient refrigerating temperature with the current density employed.

5. The combination of claim 4, in which the apparatus for operating the lamp at the proper current density is an impedance in series with the lamp.

6. The combination of claim 4, in which the apparatus for operating the lamp is an impedance in series with the lamp, and in which the electrodes are placed no more than 3 inches apart.

ORRICK H. BIGGS. 

